Circuit for electrical space discharge devices and method of operating same



June 25, 1946. J w DAWSON 2,402,607 CIRCUIT FOR ELECTRICAL SPACE DISCHARGE DEVICES AND METHOD OF OPERATING SAME Filed June 2, 1942 2 SheetsSheet 1 TIME Ts Av/zwroz.

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CIRCUIT FOR ELECTRICAL SPACE DISGHARGE' DEVICES AND METHOD OF OPERATING SAME Filed June 2, 1942 2 Sheets-Sheet 2 /NVENTQR. JOHN W DflWSO/V,

- Patented June 25, 1946 CIRCUIT FOR ELECTRICAL SPACE DIS- CHARGE DEVICES AND METHOD OF OPER- ATING SAME John W. Dawson, West Newton, Masa, assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application June 2, 1942, Serial No. 445,467 '33 Claims. (01. 315-234) This invention relates to a method of operating, and to circuits for electrical space discharge devices having pool cathodes and igniting electrodes of the resistance-immersion type, such devices being generally known as ignitrons."

Ignitrons are adaptedto be fired by pulses of electrical energy supplied to their igniting electrodes. Each of these pulses of energy is adapted to produce an incipient arc spot, which becomes a true are spot when the discharge is established within the ignitron. The igniting electrodes referred to herein are constructed of a poorly conducting or semi-conducting material, for example boron carbide or silicon carbide. This material is immersed in the cathode pool in intimate contact therein.

Heretofore the firing of ignitrons has been'limited to a frequency of the order of the frequency of the available power supply line, such as for example 60 cycles. I have discovered how to reliably fire ignitrons at a frequency of 1,000 times per second or more. To enable the firing of ignitrons at such relatively high frequencies, 1 have found that there are two critical conditions which must be met. First, there is a certain minimum critical time, for the duration of the pulses said circuits must be able to supply a given amount of current so that the incipient are spot produced by a pulse of energy of such relatively short duration may be picked up to produce a steady arc.

In order to produce an incipient are spot a certain amount of power must be applied to the igniting electrode, the amount of power required depending upon the characteristics of the ignitron employed and particularly the temperature of the igniting electrode. This power is applied for .a certain time, the amount of energy in each igniting pulse beingv equal to the product of power and time. The critical minimum time that I have the prior art and, therefore such pulses may be supplied to the igniting electrode at the rate of 1,000 or more per second without overheating the igniting electrode. However, in order that incipient arc spots produced by pulses of such short duration may be converted into true arcs, it is necessary to match the circuit supplying current to the cathode and select its constants, in accordance with the duration of the pulses. Under such conditions I have been able to fire ignitrons at the rate of 1,000'or more ignitibns per second.

An object of this invention is the provision of a method and a system for reliably firing ignitrons at relatively high frequencies, such as, for example, at a frequency of 1,000 or more times a second.

Another object of this invention is the provision of a, method and'a system of supplying pulses of electrical energy to the igniting electrode of an ignitron to produce incipient arc spots at the aforementioned relatively high frequency, without thereby overheating said igniting electrodes or causing them to lose their effectiveness.

A further object of the present invention is the provision of a circuit for supplying current to the cathode of an ignitron which enables an incipient are spot produced by a pulse of relatively short duration to be transformed into a steady arc.

Other and further objects and advantages of the present invention will become apparent and the foregoing best understood from the following description, reference being had to the drawings in which:

Figs. 1, 2, and 3 are sets of curves to which reference is made in explaining my invention, said curves being intended to express qualitatively rather than quantitatively certain aspects of my v invention; and

Fig.. 4 is a schematic diagram of a circuit in connection with which my invention is illustrated.

In order to form an incipient are spot which is capable of being transformed into a steady are, a certain minimum power must be applied to the igniting electrode. The value of this minimum power depends upon the construction of the ignitron and particularly that of the igniting electrode. This minimum value of power tends to -be of the order of 1 kilowatt with the standard igniting electrode of the resistance-immersion type. In supplying this power a voltage of about 200 volts or more is preferably applied to such igniting electrodes. Such igniting electrodes usually have aresistance of from 10-20 ohms at As stated herein'before, I have discovered that there is a minimum critical time during which power must be applied to the igniting electrode in order to form an incipient are spot. This minimum time is. of the order of .2 of a. microsecond. Referring now to Fig. 1 in which power is plotted against time, It represents the minimum critical time during which a givenpower must be applied to the igniting electrode to form an incipient are spot. Due, however; to the fluctuations in operation of ignitrons, itis preferred, in order that reliable firing may be secured, that the time during which said power is applied to the igniting electrode be longer than the critical minimum time indicated by a. It is, therefore preferred that the pulses of energy supplied to the igniting electrode have a duration of the order of 2 microseconds. However, pulses of from about 20 microseconds down to the minimum critical time may be employed in firing ignitrons at relatively high frequencies. In Fig. '1, b represents a pulse of electrical energy having a duration of the order of 2 microseconds which is a desirable value for securing reliable ignition. To further insure reliable firing the power supplied during the time indicated by b may be somewhat greater than the minimum power necessary to produce an incipient are spot.

For supplying pulses of the high frequency hereinabove indicated, various means, such as for example an oscillator, may be employed. However, I have found that the most convenient source of such pulses is the discharge from a condenser. Since it is desired that such pulses have a. relatively shortduration, the condenser employed is preferably of small capacity, for example of about .02 to. 1 microfarad. These con-.

densers are charged to a potential sufllcient to produce a pulse of the required energy content, the energy content being preferably of the order of .01 watt-second. For example, a group of condensers having the following values may be charged to the voltage indicated: 1 microi'arad at 200 volts, .25 microfarad at 260 volts, .1 microfarad at 400 volts, .05 microfarad at 800 volts, and .02' microfarad at 2000 volts.

Referring now to Fig. 1, curve represents the discharging energy of a condenser charged to a voltage as hereinabove indicated. It will be seen that the amount of energy supplied by the discharge of this condenser is of greater value than that requiredv by b, b representing the preferred value. The discharge of the condenser, as indi- 4 ohms. Of course it will be understood that while the foregoing values apply in one specific case, these may be varied to correspond to the characteristics of the particular ignitron employed, and the characteristics of the circuit in which said ignitron is employed. By using such an impedance, the size of the condenser or the amount of energy stored therein may be decreased.

Each pulse of energy supplied to the igniting electrode tends to raise the temperature of said electrode. As the temperature "of the electrode rises, more power is required in order to produce an incipient are spot. When, however, the temperature of said electrode rises above a certain critical value, the electrode will fail to produce an incipient are spot regardless of the amount of cated by curve 0, will reliably produce an incipient are spot. and the energy produced during this discharge is of such a relatively low value that the condenser may be discharged at a frequency of 1000 or more times per second without overheating the igniting electrode or rendering it inoperative. However, as will be seen by comparing curve 0 with b, a substantial amount of the energy of curvec may be eliminated by inserting' an impedance in series with the discharg- /ing condenser. The discharging energy will then 1! take the form represented by. curve d in Fig. 1. It will be seen that the power thus delivered-to n and then gradually declines. Theform of curve d approximatesmore closely the idealized form of b, and therefore less of the energy-repi niting electrode rises gradually to-its maxipower applied thereto. This failure of the igniting electrode to operate above a given temperature may be due to the fact that the material of which said electrode is made has a negative temperature coefficient of resistivity. Therefore, when the temperature of the electrode rises, its resistance diminishes; the potential gradient, which appears to be essential, according to certain theories of the operation of suchdevices, is no longer maintained.

The temperature of the igniting electrode depends on the rate at which electric energy is supplied thereto and the rate at which heat is dissipated therefrom. As the temperature of the electrode rises, the rate of dissipation of heat also tends to increase. Since each pulse of electrical energy supplied, to the electrode represents an increment of heat, if said pulses are supplied to the electrode at a rate greater than the rate of heat dissipation, the temperature of the elecrode rises and will continue to rise until a point of equilibrium is reached, at which point the rate of dissipation of heat is equal to the rate at which increments of heat in the form of electrical .energy pulses are supplied to the igniting elecrode.

According to the practice of the prior art, the total amount of energy in each pulse supplied to the igniting electrode was such that pulses could only be supplied at a comparatively low frequency. Attempts to supply such pulses at a higher frequency would produce overheating of the'igniting electrode beyond the critical temperature at which the igniting'electrod loses its effectiveness. In accordancewith myinvention thetotal each pulse, since within certain limits the H required is proportionate. to the temperature of the igniting electrode. The foregoing will be more readily understood a from the following description referring to Fig.2,

'in which temperature is plotted against time.)

Curve e of said figure represents the rise in tem- P rature of an igniting electrode during in which electrical energy of a given power is supplied thereto. It will be noted that, at a cer tain point, curve 0 intersects line 1. Line trep- I -resents approximately the critical temperature at which the igniting electrode becomes tive. It will be seen that if an electrical of a given power is delivered to the igniting electhe igniting electrode will be unable to produce an incipient are spot. In Fig. 2, line a represents the startingtemperature of the ignitingelectrode before any energy has been supplied thereto.

If a pulse of energy of a given power is applied to the igniting electrode for a short time, as for example from To-Ti, which is preferably of the order of two microseconds, it will be seen that the temperature of the igniting electrode will be raised but slightly. Thereafter, if no energy is supplied for a relatively short period Ti-T2, then, due to the dissipation of heat from said electrode, its temperature will fall back to the line g, as indicated by curve h. '11? the pulses supplied to,the igniting electrode have the-relatively short duration indicated between To--T1,

apply power to the igniting electrode for a relatively long time, such as for example that indicated by the time To-T3. Such relatively long pulses had a proportionately greater energy content and raised the temperature of the igniting electrode to a relatively higher point. In order to prevent raising of the temperature of the ig-. niting electrode to a point at which it would cease to be operative, it was necessary to wait a relatively long time TaT4 between pulses to permit theheat produced in the igniting electrode to dissipate so that the temperature of the igniting electrode would decline, for example, to line g as indicated by curve 2'. Due to the long waiting interval required, such method of operation does not permit of firing the ignitron more rapidly than at a comparatively low frequency.-

Attempts to operate at a higher frequency under such conditions will cause the temperature of the igniting electrode to rise with each pulse until finally line I is crossed and the igniting electrode becomes ineffective or burns out. i

- I have hereinabove pointed out that the igniting pulses according to my invention are of high pulse is supplied to the igniting electrode.

eflective and merely introduces heat and wastes energy. Consequently, I am able to produce incipient arc spots with greater efilciency, using a lesser amount of energy and dissipating less energy in heat in the igniting electrode.

As stated hereinbefore, the firing supplied to the igniting electrode produces incipient arc spots on the surface of the cathode pool. In order that said incipi nt arc spots may be converted into true arcs, it is essential that the current drawn from an incipient arc spot rise to a value sufllcient to sustain a true are during the period of time in which the incipient are spot is produced. In the prior art practice, in which each firing impulse had a comparatively long duration, the period of time during which the current supplied to the ignltron could rise to the required value was correspondingly long. Thus, ordiof the circuit supplying current to the ignition was unnecessary. However, when igniting pulses of such comparatively short duration as those called for by this invention are employed, the current which picks up .the arc, converting the incipient are spot into a true arc, must rise to the required value in the hereinbefore indicated short time. It therefore becomes essential to match the circuit and its constants with the length of duration of the igniting impulses.

The foregoing will be better understood with reference to the curves of Fig. 3 in which current supplied to the ignitron is plotted against time. Line '11 represents the minimum amount of current required to convert an incipient are spot into a true arc. The interval of time from Te-To represents the duration of igniting pulses in accordance with my invention, which duration may be of the order of 2 microseconds. Time Ts-T1 represents the relativelylonger duration of pulses supplied in accordance with the practice of the prior art. If curve It represents the rate at which current supplied to the ignitron can risein a certain circuit, it will be seen that the current at point P1 will have risen to the required value a substantial time before the expiration oi the pulse of igniting current indicated by TsT-r. On the other hand, it will be seen that if a circuit having the current time constants indicated by curve It is used with an ignitron to which igniting impulses of the relatively short duration indicated by T5Ts are supplied, at the end of the igniting pulse Ts-Ta the current will only have risen to the point P2 which is substantially under the minimum current value required for converting an incipient are spot into a steady are. It therefore will be apparent that where pulses of such relatively short duration are employed, a circuit having a much shorter current time constant must be employed. The constants of the circuit and the circuit employed, when using igniting pulses of such relatively short duration,

must be selected and matched with said igniting impulses. Curve 1 of Fig. 3 represents the current time characteristics of a circuit which is suitable when igniting impulses of the length of time indicated by T5Ts are employed. It will be seen that according to curve I the current rises in a comparatively short time to the line 1 which latter represents the minimum required current necessary for picking up the arc. It will be seen that point P3, where curve I meets line :i is well within the time T5--Tc during which the igniting The minimum required current for converting an incipient are spot into a true are is approximately 4 or 5 amperes with standard types or ignitrons now in use. With such ignitrons and with pulses of the duration of the order of 2 microseconds. the circuit employed must be capable of supplying a current of the order of magnitude of 4 or 5 amperes within said time of duration of the igniting impulse.

Most ignitron circuits, particularly in industrial power circuits, are incapable of supplying the required current within the time indicated. With such circuits a suitable auxiliary pick-up circuitmay be used in conjunction therewith to enable the firing of ignitrons in such circuit at a frequency of 1,000 or more times per second. A circuit employing such pick-u means is illustrated in Fig. 4, and its method of functioning will now be described in connection with said figure.

Referring now to Fig. 4. an ignitron I, having or ignitron I.

a mercury pool cathode 2, an igniting electrode 4 of the resistance-immersion type, and an anode 4' is adapted to be fired at a frequency of 1,000 or more cycles per second. Igniting impulses for this purpose are obtained from a. condenser 4 having a capacity of approximately .01 microiarad and being adapted to be charged to 400 volts. To charge condenser 4, the negative side thereof is connected to a terminal 5, and the positive side thereof is connected through a series, current-limiting resistance 6 to another terminal I. Terminals and I are adapted to be con-- nected to a suitable source of direct current supply.

To control the discharge of condenser 4, I prefer to utilize a controlled gaseous rectifying tube 4. This tube is interposed in series between the positive side of condenser 4 and the igniting electrode 3, with its anode 9 connected to the positive side of said condenser, and its cathode III connected to the igniting electrode 3. Tube I has a control grid II. The control grid II is connected to an oscillator I2 adapted to make said grid positive at the rate of 1,000 or more times per second to thereby fire tube 8 and discharge condenser 4 at said rate. To complete the igniting circuit the negative side of condenser 4 in series with condenser 4 an inductance I 3,

This inductance may have a value of to 10* henries and-a built-in resistance of the order of 0 ohms. Of course, these values may be varied to suit the particular conditions which are met.

Ignitron I may be used to control the discharge of a, relatively large condenser I4 into a load circuit I5. Since such a load circuit usually includes both inductance and resistance, it may be represented as in Fig. 4 diagrammatically by an inductance and resistance. The condenser I4 is charged with current from input terminals I8 and I? through an impedance I. which is preferably an inductance. The value of this impedance is so chosen as to maintain the proper charging rate of the condenser I4. During actual operation of this system, the impedance I8 tends to compel'the current to flow therefrom at a substantially constant value. The condenser I4 is adaptedto be discharged into the load I5 by conto one end of the load II, the other end of said load It being in turn connected to the anode 4' It willthereiore be seen that when ignitron I is fired, condenser I4 will be discharge into the load.

If, however, as stated hereinbefore, the ignitron I is to be fired at the relatively high frequency of 1,000 or more times per second, it is essential that'the current supplied by condenser I4 to said defect. Such means may consist of a pick-up circuit consisting of a condenser I9 in series with close to said ignitron.

, if ignitron I is no longer conducting. It. how;

ever, ignitron I is conducting, another complete i'gnitron rise in a very short time to a value sufllcient to convert the incipient are spot into a true arc. However, the delay in the rise of this current, due to the inductance of the load circuit, may be such as to prevent the current from rising to the required value withln'a short enough time to pick up the arc. Where the inductance inthe .circuit associated with the ignitron is of such value as to require too long a time for the rise of current supplied to the ignitron to permit the ignltron to Pick up the incipient arc spot, addi-,

- tionai means may be provided to overcome thia T It will be seen that condenser I9 is charged from terminals I8 and I1 through load I5 andresistance 20. When, thereafter, an incipient are spot is produced in ignitron I by a pulse of electrical energy supplied to the ignitingelectrode 4, condenser I9 will almost immediately begin to discharge through said ignitron. As'the current supplied by condenser I9 diminishes, the current supplied by the discharge of condenser I4 through the load will gradually rise and will thereby maintain the arc initially picked up by the discharge of condenser I9.

It will of course be understood that the pick-up circuit may be dispensed with where the load circuit is selected and matched so that itscurrent time constant is short enough to pick up the me.

Because of the inductance associated with the latory. Thus as condenser I4 discharges into the.

load the potential across said condenser falls as the current flowing from said condenser increases, until the voltage reaches a zero value at the time the current reaches its maximum. Thereafter, as the current continues to flow in the same direction the potential across said condenser reverses. The current then declines to a zero value and tends to flow in the. reverse direction. To permit this reverse flow of current, I prefer to arrange a gaseous rectifyingtube 2| in shunt across ignitron I, the cathode 22, of tube 2| being connected to anode 4" of the ignitron, and the anode 23 of tube 2| being connected with the cathode 2 01' the ignitron. The cathode 22 or tube 2| is preterably of the permanently-energized type. The

reverse current flows through tube II and the condenser again becomes charged in the original direction. v Further oscillations will be prevented cycle will occur. It will be seen that the potential across condenser I4 when the next cycle i completed is again in the same direction as the direc- I that I have provided a method and a means en-' abling the firing of ignitrons at relatively high frequencies, such as tor example of the order of 1,000 or more times per second. Furthermore, it will be seen that I have devised a method of supplying igniting impulses to the igniting electrodes of such devices at the rate 01' 1,000 or more times per second without overheating said igniting electrodes or causing'them to lose their effectiveness.

Furthermore, I have described hereinbefore how the constants oi the load circuit of such ignitrons may be selected in order to enable the ignitrons to be fired at such relatively high frequencies.

Moreover, I have shown a means whereby a load circuit having a too high current time constant may be arranged to enable it to pick up arcs from igniting impulses of relatively short duration.

Modifications will readily suggest themselves. For example, an ignitron employing an auxiliary anode may be employed. The auxiliary anode may be connected to a. source of current through a substantially non-inductive circuit. Thus the auxiliary anode will pick up the are quickly with in the time of duration of a short igniting impulse. Therefore, even if the current supplied to the main anode rises too slowly to pick up the arc from the igniting electrode, it can pick up the are from the auxiliary anode. The arrangement of such a system will be apparent to those versed in the art. Therefore, while I have described one circuit in which an ignitron is fired at the relatively high frequency characterizing my invention, it is, of course, to be understood that this circuit was described solely as an illustration, and that numerous other circuits embodying the teachings of my invention may be made. Furthermore, while I have described certain constants and indicated their values under specific conditions, it will also be apparent that certain of these values may be changed to conform to the other conditions that may be encountered. It is accordingly desired that the appended claims he given a broad interpretation commensurate with the scope of this invention within the art.

What is claimed is:

1. In the method of firing an electrical space discharge device oi the type having a pool cathode, an anode, and a resistance-immersion igniting electrode, the steps of applying a voltage between said cathode and anode for producing a flow of current therebetween, supplying igniting impulses to said igniting electrode for initiatin said current flow, and limiting said igniting impulses to a duration of the order of the critical minimum time required to produce an incipient arc spot capable of being converted into an arc.

2. In the method of firing an electrical space discharge device of the type having a pool cathode, an anode, and a resistance-immersion igniting electrode, the steps of applying a voltage between said cathode and anode for producing a flow of current therebetween, supplying igniting impulses to said igniting electrode for' initiating said current flow, and limiting said igniting impulses to a duration of the order of two microseconds.

3. In the method of firing an electrical space discharge device of the type having a pool cathode, an anode, and a resistance-immersion igniting electrode, the steps of applying a voltage between said cathode and anode for producing a flow of current therebetween, supplying igniting impulses to said igniting electrode for initiating said current flow, and limiting said igniting impulses to a duration of about twenty microseconds or less.

' 4. In the method of firing an electrical space discharge device of the type having a pool cathode, an anode, and a resistance-immersion igniting electrode, the steps of applying a voltage between saidcathode and anode for producin a flow of current therebetween, supplying igniting impulses to said igniting electrode for nitiating said current flow, and limiting saidigniting impulses to a duration of approximately from .02 to 20 microseconds.

5. In the method of firing an electrical space discharge device of the type having a pool cathode, an anode and a resistance-immersion igniting electrode, the steps of applying a voltage between said cathode and anode for producing a flow 01' current therebetween, supplying igniting impulses to said igniting electrode forinitlating said current flow, and limiting said igniting impulses to a duration of approximately from .2 to 20 microseconds.

6. In the method of firing an electrical space discharge device of the type having a pool cathode, an anode, and a resistance-immersion ignit ing electrode, the steps of applying a voltage between said cathode and anode for producing a ing electrode, the steps of applying a voltage between said cathode and anode for producing a flow of current therebetween, supplying igniting impulses to said igniting electrode for initiating said current flow, and limiting said igniting im pulses to a dura'tion of the order of two microseconds and an energy content of about .1 watt-second or less.

8. In the method of firing an electrical space discharge device of the type having a pool cathode, an anode, and a resistance-immersion igniting electrode, the steps of applying a voltage between said cathode and anode for producing a flow of current therebetween, supplyin igniting impulses to said igniting electrode for initiating said current flow, and limiting said igniting impulses to a duration of the order of two microseconds and an energy content of the order of .01

watt-second.

9. In the method of firing an electrical space discharge device of the type having a pool cathode, an anode, and a resistance-immersion igniting electrode, the steps of applying a voltage between said cathode and anode for producing a flow or current therebetween, supplying igniting impulses to said igniting electrode for initiating said current flow at the rate of 1000 or more impulses per second, and limiting said igniting impulses to a duration of the order of the critical minimum time required to produce an incipient are spot capable of being converted into an arc.

10. In the method of firin an electrical space discharge device of the type having a pool cath ode, an anode, and a resistance-immersion igniting electrode, the steps of applying a voltage between said cathode and anode for producing a' flow of current therebetween, supplying igniting impulses to said igniting electrode for initiating .said current flow at the rate of 1000 or more impulses per second, and limiting said igniting impulses to a duration of the order of two microseconds.

11. In the method of firing an electrical space and means for supplyi 11 I onds an an energy content oi. about .1 watt-second or less.

12. In the method of firing an electrical space I discharge device of they type having n anode, a

pool cathode, and a resistance-immersion igniting electrode, the steps of supplying igniting impulses to said igniting electrode, limiting said igniting impulses toa duration 01 the order of 3. In the method of firing an electrical space discharge device of t e type having an anode,

a pool cathode, and a resistance-immersion igniting electrode, the steps of supplying igniting impulses to said igniting electrode, limiting said igniting impulses to a duration of the order of two microseconds, supplying current surges between said anode and cathode, and causing said current surges to rise to at least the minimum critical value required to pick up the are within said time of duration of the igniting impulses.

"14. In the method of operating an electrical system including an electrical space discharge device of the type having at least an anode, a pool cathode, and a resistance-immersion igniting electrode, and a circuit for supplying current to said cathode, the steps of supplying igniting impulses to sa'icl igniting electrode, limiting said igniting impulses to a duration of the order of the critical minimum time required to produce an incipient arc spot capable of being converted into an arc, supplying current surges to said cathode, and causing said current surges to rise to at least the minimum critical valueirequired to pick up the are within said time of duration or the igniting impulses.

15. In the method of operating an electrical system including an electrical space discharge device of the type having at least an anode, a pool cathode, and a resistance-immersion igniting electrode, and a circuit for supplying current to said cathode, in which load circuit current can rise only at a relatively slow speed, the steps 01 supplying igniting impulses to said igniting electrode, limiting said igniting impulses to a duration of the order of two microseconds, supplying current surges between said anode and cathode, and causing said current surges to rise to at least the minimum critical value required to pick' up the are within said time of duration 01' the igniting impulses, and to have a duration sufiicient to maintain the arc until the current from said load circuit has risen to the value necessary to continue said arc. I

16., In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersionigniting electrode, and means for supplying igniting impulses to said igniting electrod a duration of the order of the critical minimum capable of being converted into an arc.

, said igniting impulses having;

- second or less, and means for discharging said 17. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, igniting. impulses to said igniting electrode, said igniting impulses having a duration of the order of two microseconds.

18. In combination, an electrical space discharge device having ananode, a pool cathode,

and a resistance-immersion igniting electrode, and means for supplying igniting impulses to said igniting electrode, said igniting impulses having a duration of about twenty microseconds or less.

19.In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, and means for supplying igniting impulses to said igniting electrode, said igniting impulses having a duration of approximately from .02 to 20 microseconds.

20. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, and means for supplying igniting impulses to said igniting electrode, said igniting impulses having a duration of approximately from .2 to 20 microseconds.

'21. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, and means for supplying igniting impulses to said igniting electrode, said igniting impulses having a duration of the order of the critical minimum time-required to produce an incipient arc spot capable of being converted into an arc and an energy content of about .1 watt-second or less.

22. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, and means for supplying igniting impulses to said igniting electrode, said igniting impulses having a duration of the order 01' two microseconds and an energy content 01' about .1 watt-second or less.

23. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, and means for supplying igniting impulses to said igniting electrode, said igniting impulses having a duration of the order of two microseconds and an energy content of the order of .01 watt-sec- 0nd.

24. In combination, an electrical space discharge device having an anode, a-pool cathode, and a resistance-immersion igniting electrode, and means for supplying igniting impulses to said igniting electrode at the rate of 1000 or more impulses per second, said igniting impulses havcharge device having an anode, a pool cathode,

and a resistance-immersion igniting electrode, and means for supplying igniting impulses to said igniting electrode at the rate 01' 1000 or. more impulses per second, said igniting impulses having an energy content of the order of .01 wattsecond.

26. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, means for supplying igniting impulses to said igniting electrode, said means including a condenser having a capacity or the order or the range of from .02 to 1 microfarad and adapted to" be charged to an energy value of .1 wattcondenser through said igniting electrode.

2'7. In combination, an electrical space discharge device having an anode, a pool cathode,

and a resistance-immersion igniting electrode,

means forsupplying igniting impulses to said igniting electrode, said means including a condenser having a capacity of about one microi'arad charge device having an anode, a pool cathode,

and a resistance-immersion igniting electrode,

means for supplying igniting impulses having aduration of the order of two microseconds to said igniting electrode, and a circuit for supplying surges of current to said cathode, said circuit having a current time constant sufficiently small to supply within the time of duration of one of said igniting impulses sufilcient current to establish an arc.

30. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, means for supplying igniting impulses having a duration of the order of two microseconds, and

a circuit for supplying surges of current to said cathode, said circuit being capable of supplying within the time oi duration of one oi said igniting impulses suillcient current to establish an arc.

31. In combination, an electrical space "discharge device having 'an anode, a pool cathode, and a resistance-immersion igniting electrode, means for supplying igniting impulses having a duration of the order of two microseconds. a circuit for supplying surges or current between said anode and cathode, said circuit being incapable of supp s wi the time of duration of one an electrical ensgy storage means, connected to feed energy between said cathode and anode, said storage meansbeing sunlciently large and the impedance of said auxiliary circuit to current surges being sufllciently small to produce a current surge between said anode and cathode oi l4 sunicientmagnitudetoestablishanarcuponsaid igniting electrode being supplied with an igniting impulse.

32. In combination, an electrical space discharge device having an anode, a pool cathode, and a resistance-immersion igniting electrode, means in supplying igniting impulses having a duration 0! the order of two microseconds. a circuit for supplying surges of current between said anode and cathode, said circuit being incapable of supplying, within the time of duration of one of said igniting impulses. suiiicient current to establish an arc, and an auxiliary circuit, including an electrical energy storage means, connected to feed energy between said cathode and anode. said storage means being sufliciently large and the impedance of said auxiliary circuit to current surges being sufllciently small toproduce a current surge between said anode and cathode, within the time of duration of one of said igniting impulses, oi sufllcient magnitude to establish an are upon said igniting electrode being supplied with an igniting impulse.

, 33. In combination, an electrical space discharge device having an anode, a pool cathode. and a resistance-immersion igniting electrode. means for supplying igniting impulses having a duration of the order of two microseconds, a circuit for supplying surges of ,current between said anode and cathode. said circuit being incapable of supplying within the time of duration oi one of said igniting impulses suflicient current to establish an arc, and an auxiliary circuit including an electrical energy storage means connected to teed energy. between said cathode and anode, said storage means being sufliciently large and the impedance of said auxiliary circuit to current surges being sumciently small to produce a current surge between said anode and cathode. within the time of duration of one of said igniting impulses, of sumcient magnitude to establish an at said igniting impulses suiiicient current to establish an arc, and an auxiliary circuit, including.

are upon said igniting electrode being supplied with an igniting impulse, said auxiliary circuit being capable of supplying at least sumcient currenttomaintainsaidarcuntilthecurrentinthe main circuit has risen to a value sumcient to sus- JOKN W. DAWSON. 

